Gas turbine engines operate by passing a volume of high energy gases through a plurality of stages of vanes and blades, each having an airfoil, in order to drive turbines to produce rotational shaft power. The shaft power is used to drive a compressor to provide compressed air to a combustion process to generate the high energy gases that ultimately provide thrust. Additionally, the shaft power can be used to drive a generator for producing electricity. In order to produce gases having sufficient energy to drive the compressor or generator, it is necessary to combust the fuel at elevated temperatures and to compress the air to elevated pressures, which again increases the temperature. Thus, the vanes and blades are subjected to extremely high temperatures, often times exceeding the melting point of the alloys comprising the airfoils.
In order to maintain the airfoils at temperatures below their melting point, it is necessary to, among other things, cool the airfoils with a supply of relatively cooler air typically bled from the compressor. In particular, relatively cool air from the compressor is used to cool hotter components in the turbine system. Typically, the compressor air is taken from the discharge section of the compressor so that the air is sufficiently pressurized to route to other locations in the engine. The compressor air can be directly routed to hot components such as the turbine, as is known in the art. Alternatively, the compressor air can be routed to a heat exchange system that further cools the compressor air, as is shown in U.S. Pub. No. 2002/0310955 to Norris et al., which is assigned to United Technologies Corp. In high performance engines, for example, the compressor vanes and blades themselves sometimes need to be cooled with the cooled compressor air because high engine operating pressure ratios increase the discharge temperature of the compressor.
The cooled compressor air can be routed to hot components by passing the air through the engine casing, radially outward of the primary gas path, until it reaches the desirable axial position within the engine. Sometimes it is desirable to route the air radially inward of the primary gas path, through the rotating components of the engine. For example, after being cooled by the heat exchange system, the cooled compressor air is sometimes routed through the engine to cool the interface between airfoils and the rotors to which they are mounted, as shown in U.S. Pat. No. 6,655,920 to Beutin et al. Rotation of the cooling air caused by rotation of the engine components, however, induces thermal losses into the cooling system, thereby reducing the overall engine efficiency. There is, therefore, a need for reducing efficiency losses in gas turbine engine air cooling systems.